149 



On a New Aulacodiscus, from the West Coast of 



Africa. 



By Arthur Cottam, P.R.A.S. 



(Read February 2oth, 1876.) 



A.n extraordinary diatomaceous gathering has recently been 

 brought to England, from the West Coast of Africa, by Mr. 

 Martin, an Officer of H.M.S " Spiteful," made by bim when that 

 vessel was sent with the Expedition up the River Congo, at a place 

 called Banana Creek. The peculiarity of tins gathering is that it 

 consists of one species only, in countless tbousands, without any 

 admixture whatever either of other diatoms or of any foreign 

 matter ; and I believe he describes the quantity obtained as " about 

 a pint." 



Tbe diatom so gathered is a species of Aulacodiscus — a genus, 

 no member of wbich is very common, and most are decidedly rare. 



When it was first seen by our leading diatomists it was with one 

 consent dubbed a variety, and an exceedingly beautiful one, of that 

 rare form A. Kitioni. But in November last Mr. Kitton him- 

 self wrote to me to say that, having looked over his slides of 

 Aulacodisci he had found a specimen of A. Johnsonii, from Algoa 

 Bay guano, that was identical with the so-called variety of 

 A. Kittoni. 



This letter excited my curiosity to see a specimen of A. John- 

 sonii from Algoa Bay guano, but they are very scarce; only the 

 first sample of the guano that was brought to England having 

 contained it, and only a small number were found in that. My 

 cousin, Mr. Arthur C. Cole, of Liverpool, very kindly lent me his 

 only specimen, and my good friend Mr. George Mansfield Browne, 

 also of Liverpool, most generously presented me with another ; and 

 it afterwards occurred to me that the late Dr. Grev;lle's collection 

 in the British Museum was sure to contain some. I therefore went 



